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// Tests the behavior of explain() when used with the aggregation pipeline and limits.
//
// This test makes assumptions about how the explain output will be formatted, so cannot be
// transformed to be put inside a $facet stage, or when pipeline optimization is disabled.
// @tags: [do_not_wrap_aggregations_in_facets,requires_pipeline_optimization]
(function() {
"use strict";
load("jstests/libs/analyze_plan.js"); // For getAggPlanStages().
let coll = db.explain_limit;
const kCollSize = 105;
const kLimit = 10;
// Return whether or explain() was successful and contained the appropriate fields given the
// requested verbosity. Checks that the number of documents examined and returned are correct given
// the value of the limit.
function checkResults({results, verbosity}) {
let cursorSubdocs = getAggPlanStages(results, "LIMIT");
assert.gt(cursorSubdocs.length, 0);
for (let stageResult of cursorSubdocs) {
assert.eq(stageResult.limitAmount, NumberLong(kLimit), results);
if (verbosity !== "queryPlanner") {
assert.eq(stageResult.nReturned, NumberLong(kLimit), results);
}
}
// Explain should report that we only have to examine as many documents as the limit.
if (verbosity !== "queryPlanner") {
if (results.hasOwnProperty("executionStats")) {
assert.eq(results.executionStats.nReturned, kLimit, results);
assert.eq(results.executionStats.totalDocsExamined, kLimit, results);
} else {
// This must be output for a sharded explain. Verify that each shard reports the
// expected execution stats.
assert(results.hasOwnProperty("shards"));
for (let elem in results.shards) {
const shardExecStats = results.shards[elem].executionStats;
assert.eq(shardExecStats.nReturned, kLimit, results);
assert.eq(shardExecStats.totalDocsExamined, kLimit, results);
}
}
}
}
// explain() should respect limit.
coll.drop();
assert.commandWorked(coll.createIndex({a: 1}));
for (let i = 0; i < kCollSize; i++) {
assert.commandWorked(coll.insert({a: 1}));
}
const pipeline = [{$match: {a: 1}}, {$limit: kLimit}];
let plannerLevel = coll.explain("queryPlanner").aggregate(pipeline);
checkResults({results: plannerLevel, verbosity: "queryPlanner"});
let execLevel = coll.explain("executionStats").aggregate(pipeline);
checkResults({results: execLevel, verbosity: "executionStats"});
let allPlansExecLevel = coll.explain("allPlansExecution").aggregate(pipeline);
checkResults({results: allPlansExecLevel, verbosity: "allPlansExecution"});
// Create a second index so that more than one plan is available.
assert.commandWorked(coll.createIndex({a: 1, b: 1}));
plannerLevel = coll.explain("queryPlanner").aggregate(pipeline);
checkResults({results: plannerLevel, verbosity: "queryPlanner"});
execLevel = coll.explain("executionStats").aggregate(pipeline);
checkResults({results: execLevel, verbosity: "executionStats"});
allPlansExecLevel = coll.explain("allPlansExecution").aggregate(pipeline);
checkResults({results: allPlansExecLevel, verbosity: "allPlansExecution"});
})();
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